Frequency changing apparatus



Aug. 14, 1934.

L. A. GEBHARD FREQUENCY CHANGING APPARATUS Filed Deo. 6, 1932 I ,....M..www

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90m QL, www@ ATTORNEY L. A. GEBHARD FREQUENCY CHANGING APPARATUS Aug. 14, 1934.

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Patented ug. 14, 1934 UNITED STATES PATENT Folv-*Fics FREQUENCY CHANGING APPARATUS Louis A. Gebhard, Washington, D. C.

Application December 6,

9 Claims.

1932, serial No. 645,962 l My invention relates broadly to high frequency signal transmission systems and more particularly to a structure of frequency changing apparatus of high efficiency.

One of the objects of my invention is to provide a construction of high frequency transmitter adapted for operation over a relatively wide frequency band and having means for electrically and magnetically isolating unused inductance units from the selected inductance unit which is employed for operation in the transmitter for securing a high degree of eiciency in the transmission of signals.

Another object of my invention is to provide means for electrostatically shielding sets of inductance units of different frequency characteristics in a transmission system with means for short-circuiting the turns of inductance units not employed in the transmission circuit for preventing undesired losses due to resonant effects and eddy currents which would otherwise be produced in the unused inductanceV units adjacent the selected inductance unit.

Still another object of my invention is to provide means for electrically and magnetically isolating unused inductance units from a selected inductance unit in a frequency changing apparatus for a high frequency transmitter for insuring maximum efficiency in signal transmission.

Other and further objects of my invention reside in the construction of a frequency changing apparatus for high frequency transmitters, as*r set forth more fully in the specification hereinafter following by reference to the accompanying drawings, in which:

Figure 1 is a longitudinal cross-sectional view taken through the inductance system of a transmitter embodying my invention, the View being taken on line l-1 of Fig. 4; Fig. 2 is a side elevational view of the switching mechanism employed in the frequency changing apparatus of my inventionl the electrostatic shield for the frequency changing apparatus being shown in crosssection on line 2-'2 of Fig. 1; Fig. 3 is a side elevational view showing part of the contact system for the switching mechanism taken on line `3--3 of Fig. 4 with the frame structure shown in ycross section; Fig. 4 is a top plan view showing one of the inductance units and coacting switching mechanism, with the electrostatic shield and the frame structure shown in horizontal cross section; Fig. 5 is front elevational view of one of the control switches employed for selecting a particular inductance unit; and Fig'.A 6 shows a circuit arrangement for a push pull amplifier system employing the frequency changing apparatus of my invention. n

In a high frequency transmitter covering such a wide frequency band that it is necessary to have a number of coils in the input and output circuits in order to cover the required band, it is desirable to have these coils mounted permanently in the transmitter instead of plugging them in and keeping the spare coils outside the transmitter around the radio room. When a number of coils are placed in a high frequency transmitter, unless they are isolated from one another, they are liable to cause trouble due to resonant effects. If the power is suflicient, excessive voltages may be set up in the unused coils such as to cause the breakdown ofthe insulation of these coils. At these resonant points the efficiency may be very low due to the power consumed in the unused coils. It is possible that the balancing of the amplifier circuits in which these coils are used may be seriously affected. One way of isolating the coils would be to space them far enough apart. This however isimpossible in a high frequency transmitter since in this type of transmitter the leads between the coils and the adjacent circuits must be very short. In fact in certain cases the total length of the conductor in the coil itself is but a foot or two. In the frequency changing apparatus of my invention, I provide a multiplicity of electrostatically shielded compartments enclosing inductance units of different frequency characteristics, each inductance unit being provided with selected taps and switching means adjacent thereto for selecting a particular inductance unit andrendering such inductance unit effective in associated oscillation circuits, or electrically short-circuiting the turns of unused inductance units and connecting such inductance units to be ground lpotential for preventing undesired losses from unused indutance units in the vicinity of the effective inductance unit.

Referring to the drawings in more detail, reference character 1 designates a multiplicity of inductance units of different frequency characteristics. While I have only illustrated four such units, it is understood that any number of units may be employed in accordance with the frequency range of the transmitter. The inductance units 1 are mounted within electrostatically shielded compartments 2 having walls of sheet metal. The compartments electrostatically isolate the inductance units l from each other and from adjacent oscillation circuits. I provide suitable supports of insulation material represented at 3 for mounting the inductance l. The inductance units which are provided with taps 25 are electrically connected in circuit with the oscillation system through switching mechanism which is enclosed in the respective electrostatically shielded compartments. The switching mechanism includes insulated shaft 20 to which there extends a multiplicity of taps 25 connected to adjacent turns of the inductance units. Switch blades 8 are carried on shaft 20 by bushing `members indicated at 24 in immediate electrical connection with the taps 25. The coils are connected in the circuit by the actuation of switches 4. The switch blades are contained entirelywithin the shielded compartment 2, formed in part by the -frame structure 40 of the transmitter, except when they are connected, in which case the ends of the switches project through slots 5 in shield 6 so as to make connection with contacts 7. When the coils are disconnected from the circuit they are each short circuited by movement of switch blades 8 into connection with contacts 9 which are mounted on the upper portions of electrostatically shielded compartments 2. Thus any coupling due to the capacity between the ends of switch blades 8 and contacts 7 is avoided. 'I'he coils are not alone short circuited but are also grounded to the shield forming the compartments 2 by means of engagement of the switch blades 8 with contacts 9 which are mounted on the shields. The coil system 1 is shown as applied to the output circuit of a high power high frequency push-pull amplifier system mounted within the frame structure 40 and wherein the electron tubes are indicated at 10 and 10', the output tuning and balancing condensers at 11, and the adjustable portion of the tuning condenser at 12.

In the use of such an amplifier system it is desirable to use five tap points on the inductance coils, the two outer points being for tuning connections, the center tap being for plate voltage connection, the other two connections being for coupling connections. The tuning connections contact groups are shown at 13 and 13'. The power connection contact group is shown at 14. The coupling connection contact groups are shown at 15 and 15'. The contact groups 13 and 13' are shown supported directly from the tuning condenser 11. The contact groups 14, 15 and l5 are shown supported on insulating members 16 and 16. The contacts of each group are connected in parallel. Those of the groups 13 and 13' are connected together by use of the surface of the tuning condenser. Those of groups 14, 15 and 15' are connected together by vertically disposed metallic busses shown at 17. These busses are in turn supported by insulating members 16 and 16. The insulating members 16 and 16' are fastened to the front panel 18 and yrear panel 18' by means of angle members 19 and 19'. The switches are supported on insulated shafts 20 rotating in bearings 21 and 21' mounted on panels 18 and 18'. These shafts are controlled by knobs 22 located on the front of the front panel 18. An indicator 23 is provided to indicate whether the selected inductance coil is connected in or out of the circuit. The number shown at 38 placed above the switch 22 on panel 18, identiiies the particular coil unit which is employed. The switch blades 8 are secured to the shaft by the use of bushing members 24 which make connection with the coil units 1 through links 25 and thus establish connection to the switch blades 8.

The slots 5 in panel 6 are made as small as possible so as to reduce the electric field to the coil contacts and coil to a minimum. They must be made large enough, however, to prevent arcing, or sparking over, due to the voltages between the blades of the switches 8 and the grounded shield 6. It will be observed that not only can any selected inductance coil be connected in the circuit but two or more inductance coils may be placed in parallel should this be desired.

Fig. 6 shows the frequency changing system of my invention in which a push-pull balanced amplifler system is employed. An input circuit is shown at 26, balancing condensers at 27 and 27', the tuning condenser at 28, antenna coupling condensers at 29 and 29', and a doublet antenna or other load circuit at 30. The coil 1 is shown connected in the circuit through contacts 7 and contact bars 13, 13', 14, 15 and l5'. It should be noted that in this system the side shield 31 is used as a shield for the end of the radio transmitter as Well as a shield for the coil units.

The system of my invention enables the `selected inductance unit to be electrostatically and magnetically isolated from adjacent inductance units for avoiding undesired coupling with the unused inductance units with the accompanying losses in radio frequency current by virtue of the substantially complete enclosure of each inductance unit within a metallic casing formed by six coacting electrically conductive walls surrounding each inductance unit. The contact elements which are located outside of the electrostatically shielded compartments provide extremely short connections to other portions of the oscillatory system, thereby maintaining a high degree of efficiency. The connection between the oscillating circuit and the selected inductance unit is maintained extremely short. The conductors are of such size as to avoid losses. static shield to the inductance units does not require the addition of any appreciable length `to the leads as the switch blades are relatively short. I have shown the several compartments arranged in stacked relation but it will be understood that the compartments may extend horizontally when it is possible to assemble the induc tance units more compactly with respect to the remaining parts of the transmitter.

While I have described my invention in one of its preferred embodiments, I desire that it be understood that modifications may be made and that no limitations are intended other than are imposed by the scope of the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalty thereon or therefor.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. Frequency changing apparatus comprising an electrically shielded structure including a plurality of compartments, inductance units of different frequency characteristics, one of said inductance units being disposed in each of said compartments, a switch individual to each of said compartments, contact members disposed outside of each of said compartments in alignment with the path of movement of each of said switches, each of said compartments being slotted adjacent said contact members for the passage of said switches through the side wall thereof for establishing electrical connection with each of said contact members, said switches being connected to taps on said inductances.

2. Frequency changing apparatus for high frequency signaling systems comprising a multiplicity of electrostatically shielded compartments, inductance units of different frequency characteristics, one of said inductance units being disposed in each of said compartments, a switch member mounted in each of said compartments, a multiplicity of coacting contact elements disposed outside oi said compartments in alignment with said switch members, said switch members being selectively movable for establishing connection 'I'he addition of the electro-l between taps on each of said inductance units and the coacting contact elements outside of saidA compartments.

3. In a frequency changing system, a multiplicity of electrostatically shielded compartments, inductance units of diiferent frequency characteristics, one of said inductance units being disposed in each of said compartments, a rotatable switch member in each of said compartments, a multiplicity of coacting contact elements adjacent said compartments and aligned with each of said switch members, a grounded contact in each of said compartments, and means for selectively shifting said switch member from a position electrically connecting said grounded contacts to a position establishing connection between taps on said inductance units and said coacting contact elements outside of said compartments.

l` Frequency changing apparatus comprising a multiplicity of electrostatically shielded compartments, inductance units of different frequency characteristics, one of said inductance units being insulatingly supported in each of said compartments, a rotatable shaft of insulating material disposed in each of said compartments adjacent the inductance units therein, contact members extending toward each of said shafts from taps on said inductance units, switch blades carried by said shafts and aligned for establishing electrical connection with said contact members, coacting contact elements outside of' said compartments aligned with the path of movement of said switch blades, contact elements grounded to each of said compartments and disposed in. the path of movement of said switch blades, and means for shifting said switch blades from connection with the grounded contact elements within said compartments to a connection with the coacting Contact elements outside of said compartments.

5. Frequency changing apparatus comprising a multiplicity of electrostatically shielded compartments, inductance units of different frequency characteristics, one of said inductance units being insulatingly supported in each of said compartments, taps on said inductance units, switch blades electrically connected with said taps, contact members grounded to the wall of each of said compartments, coacting contact members exterior to each of said compartments and disposed in the path of movement of said switch blades, and means for selectively shifting said switch blades for establishing electrical connection between the switch blades connected with the taps on one of said inductance units and the coacting contact members exterior to said compartments while effecting a short circuit across the taps of the others of said inductance units.

6. Frequency changing apparatus comprising a multiplicity of electrostatically shielded compartments, inductance units of different frequency characteristics, one of said inductance units being insulatingly supported in each of said compartments, a rotatable shaft of insulating material journaled Within each of said compartments adjacent the inductance unit therein, switch blades carried by each of said shafts, connections between each of said switch blades and taps on the adjacent inductance unit, grounded Contact clips carried by a wall of each compartment and disposed in the path of movement of the switch blades carried by the rotatable shaft in the said compartment, and coacting contact clips exterior to each of said compartments in the path of movement of the switch blades carried by the rotatable shaft in the said compartment. and

means for angularly moving each of said shafts for transferring connections between said switch blades, said grounded contact clips and said coacting contact clips exterior to said compartments.

'7. Frequency changing apparatus comprising a multiplicity of electrostatically shielded compartments, inductance units of different frequency characteristics, one of said inductance units being insulatingly supported in each of said compartments, bus bars extending parallel to one wall of said compartments, coacting contact clips carried by said bus bars, a rotatable switch actuator in each of said compartments, rotatable switch blades operated by said actuators, grounded contact clips in each of said compartments, connections between said switch blades and taps on an adjacent inductance unit, and means for selectively moving said switch blades from positions electrically connecting said grounded contact clips to positions establishing electrical connection with the coacting contact clips on said bus bars exterior to said electrostatically shielded compartments.

8. Frequency changing apparatus comprising a plurality of electrostatically shielded compartments aligned adjacent each other, inductance units of different frequency characteristics, one of said inductance units being insulatingly supported in each of said compartments, a plurality of bus bars extending parallel to one side oi said compartments, coacting contact clips carried by said bus bars, a switch actuator movable to either of two limiting positions and extending through each of said compartments adjacent said inductance units, switch blades carried by said actuators and connected with taps on each of said inductance units, grounded contact clips connected with one wall of each of said compartments and disposed within the limit of the path of movement of said switch blades in one direction, the coacting contact clips on said bus bars being disposed within the path of movement of said switch blades adjacent the limit of the path of travel of said switch blades in the opposite direction whereby a selected inductance unit may be rendered electrically effective while the adjacent inductance units are short circuited.

9. Frequency changing apparatus comprising a plurality of electrostatically shielded compartments disposed in stacked relation, inductance units of diiferent frequency characteristics, one of said inductance units being nsulatingly supported in each of said compartments, a plurality of bus bars extending parallel to one side of said compartments, coacting contact clips carried by said bus bars, a switch actuator movable to either of two limiting positions and extending through each of said compartments adjacent said inductance units, switch blades carried by said actuators and connected with taps on each of said inductance units, grounded contact clips con nected with one wall of each of said compartments and disposed within the limit of the path of movement of said switch blades in one direction, the coacting contact clips on said bus bars being disposed within the path of movement of said switch blades adjacent the limit of the path of travel of said switch blades in the opposite direction whereby a selected inductance unit may be rendered electrically effective while the adjacent inductance units are short circuited.

LOUS A, GEBHARD. 

